[Histonet] Movat Stain Ferric Chloride Solution Color?

[John Kiernan]

Check with a pH meter. The ferric chloride solution in water is close to 0.1M and should have pH=2.
5ml of conc. HCl in 500ml of water is also about 0.1M, with pH=1.
The change in colour from orange to yellow is due to further acidification. The acidified (yellow) solution keeps for years, but a pale precipitate forms slowly (weeks to months) in unacidified FeCl3 solutions. 

My guess is that your supply of conc. HCl is no longer conc. enough to change the colour of the FeCl3. Checking the pH should confirm. Remember that the electrode may take some time (minutes) to equilibrate at low pH. 

John Kiernan
London, Canada
= = =
On 09/04/15, Jerry Ricks  <rosenfeldtek <@t> hotmail.com> wrote:
> I do a lot of Movat Pentachrome stains. Every once in a while something goes wrong!
> 
> I just made a solution of Ferric Chloride as follows: Dissolve 12.4 grams Ferric Chloride Hexahydrate in 500 ml dH2O. THen add 5.0 ml of concentrated Hydrochloric acid.
> 
> What is troubling me is that the solution usually starts of brownish, then turns clear yellow after I add the HCl. This time is stayed brownish and didn't turn yellow.
> 
> Seems like 15 years ago we did a Movat where someone hadn't added the HCL to the solution, it staed brown, and the Weigerts part of the stain didn't work.
> 
> Any ideas? I'm sure I added the HCl.
> 
> 
> Jerry L Ricks
> Research Scientist
> University of Washington
> Department of Pathology
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